The conventional endocardial lead, much used with cardiac pacemakers, has one end electrically connected into a socket in the pacemaker and has a tantalum wire sleeved within a silicone tube for electrical connection to a conductive tip, or exposed electrode.
The conventional electrode of an endocardial lead is of rigid, electrically conductive, metal, and may be of ball shape. Because such conventional electrodes have been relatively blunt at the leading tip, insertion thereof into a vein and threading the endocardial lead along the vein into the ventricle chamber of the heart has been somewhat difficult. It is desirable for the electrode to be inserted until it is in the apex of the right ventricle chamber of the heart. Occasionally the conventional electrode has pierced the wall of the chamber or has been inadvertently drawn rearwardly away from its apex position.
It has heretofore been proposed as in U.S. Pat. No. 3,664,347 to Harmjanz of May 23, 1972, to provide a portion of the filament of an endocardial lead which extends beyond the electrode, thereby forming a flexible tail section that helps to hold the electrode at a desired position within the heart. However, the lead is "bi-polar" rather than "unipolar," so that intimate contact of the exposed surface of a single electrode is not required and the bi-polar lead can float in the heart without touching the surface of the heart, while being anchored through a valve into a lung.
It has been my experience that attempting to follow such teaching with a uni-polar lead may cause terminal vibration, or drilling, action giving rise to bruises and that a sliding contact is more desirable.
A bi-polar lead is disclosed in U.S. Pat. No. 4,046,151 to Rose of Sept. 6, 1977, the tip having a corkscrew for penetration into the wall of the heart, thereby risking infection, fibrosis and entailing difficulty in removal.
In U.S. Pat. No. 4,033,357 to Helland of July 5, 1977 prongs, or tines are provided to lodge the tip of a bi-polar lead in the trabeclae of the right ventricle of the heart.